The present invention generally relates to surgical instruments, and more particularly to surgical instruments used in arthroscopic surgery.
Arthroscopic surgery is typically performed through very small incisions to enable a surgeon to examine a joint and perform certain surgical procedures on a joint through the small incisions. Arthroscopic surgery is typically performed through three small one-fourth inch incisions while the patient is under general anesthesia. A fiber optic telescope or arthroscope, smaller than the size of a pencil, is inserted into one of the incisions for allowing the surgeon to thoroughly examine all parts of the joint. A small television camera may be attached to the arthroscope and the magnified image of the inside of the joint is displayed on a television screen. Small delicate instruments are inserted through one of the other small incisions, and the damaged portion of the joint may be repaired or corrected. The small incisions avoid the large scars of a conventional open surgical operation and shorten the patient's recovery time while reducing postoperative pain.
One such small instrument often used in arthroscopy is a cutting instrument. As is known in the art, the use of a protective sheath provides a means of atraumatic insertion of the cutting instrument into the body to the actual cutting site. This minimizes the chance of accidental cutting of surrounding tissue. The cutting blade is attached to a blade handle, and is maintained retracted within the sheath prior to use. After positioning of the distal end of the sheath near the cutting site, the blade and blade handle may be moved forward within the sheath to expose the cutting edge or blade from the distal end of the sheath.
An example of a prior art surgical knife/sheath combination is shown in FIGS. 1, 2, and 3 herein. This device provides two functional positions for the handle relative to the sheath. In one position, the blade attached to the handle is exposed for cutting and in the other position, it is withdrawn completely within the protective sheath for insertion or withdrawl. The blade handle with the blade secured thereto is introduced into the sheath through its proximal end until the handle is locked into either of the two positions. This insertion of the blade from the proximal end through the length of the sheath undesirably exposes the blade to dulling by contacting the inner walls of the sheath throughout the length of the sheath as the blade is advanced toward the distal end of the sheath. Also, when a new blade is required, the blade handle must be completely removed from the sheath, the blade changed and the blade handle reinserted through the sheath, again risking dulling of the new blade.
In this prior art device, the mechanism for selectively positioning or locking the blade handle in position with respect to the sheath is a mechanism which is external to the sheath. The blade handle includes an enlarged proximal portion with one end of a cantilever spring mechanism attached thereto and extending toward the distal end of the blade handle. A knob (including a protruding pin portion) is attached to the opposite end of the cantilever spring mechanism. A slot is provided on the proximal end of the sheath which enables the cantilever spring to remain external to the sheath as the blade handle is inserted. The protruding pin on the knob may then be positioned in either one of two corresponding holes provided in the sheath. The proximally located hole corresponds to the retracted blade position and the distal hole corresponds to the exposed blade position. The blade handle can not be extended any further than this exposed position. This arrangement disadvantageously requires both hands of the surgeon to change the blade handle from one position to the other: one hand to hold the sheath and the other to pull up on the knob and slide the blade handle to the appropriate position.